The overall goal of this NCVDG proposal is to develop an efficacious vaccine against human immunodeficiency virus (HIV), the etiological agent of AIDS. The vaccines under development in this project include (1) live recombinant poxviruses expressing multiple HIV-1 antigens and (2) HIV- like particles produced in vitro by recombinant poxviruses expressing multiple HIV-1 antigens. In order to allow evaluation of candidate vaccines for protective efficacy, recombinant SIV vaccines will be developed simultaneously and in parallel with HIV vaccine. In previous studies, a number of recombinant vaccinia viruses, for immunogenicity in these animals. In the current research plan, these studies will be extended to generate improved vaccines with greater potential for eliciting protective immunity. The aims of this program are the following: (1) To generate new live recombinant vaccinia-based vaccines; (2) To evaluate alternate poxvirus vectors, namely fowlpox virus and swinepox virus, for use as live recombinant vaccines: (3) To generate improve poxvirus recombinants for the generation of lentivirus-like particles. To assess the possibility that protection requires immunity to viral gene products other than those encoded by env, gag, and pol, SIC/vaccinia recombinants that express these additional gene products will be generated for evaluation in macaques. Additionally, in order to maximize host immune responses to vaccinia-expressed antigens and/or increase the safety of the recombinants, HIV and SIV antigens will be co-expressed with selected cytokines. Recombinant fowlpox virus and swinepox virus, which are host-range restricted to birds and swine, respectively, will be generated for evaluation in animal models. Finally, HIV/vaccinia recombinants for human clinical trials will be developed which contain multiple HIV genes, including env genes from the major HIV subtypes. Recombinant poxviruses will be used for the production of virus-like particles in vitro. These particles will be used individually and in combination with poxvirus recombinants as vaccine immunogens. Furthermore, in an effort to increase the quantity and quality of HIV- like particles produced by recombinant poxviruses, the effect of the regulatory genes vpu and vif in the vaccina-directed expression of HIV- like particles will be examined.